Conventionally, for storage and delivery of electronic components such as IC chips and surface mount components, a carrier tape has been widely used, in which pockets processed to have recesses conforming to the shape of electronic components are formed successively. Once the electronic components are housed in the recessed pockets of carrier tape, the recessed pockets are sealed using a heat-sealable cover tape, to prevent falling of electronic components during delivery and to protect the electronic components against foreign matter in the environment.
Recently, in order to improve productivity by making shorter the time for heat-sealing and to stabilize the state of heat-sealing, a cover tape has been desired that poses no problem in production even if heat-sealing temperature and heat-sealing pressure are set higher than conventionally used.
Further, the reduction in size of electronic components has made it necessary to form the pockets of the carrier tape smaller. To meet such demands, attempts have been made to improve processability and strength of the pockets mentioned above, by changing the material for carrier tape from conventionally used polystyrene-based material to engineering plastic materials such as polycarbonate-based resin having higher rigidity. The engineering plastic resin, however, has higher softening temperature than polystyrene and, therefore, heat-sealing temperature must be made higher than conventionally used, in order to attain sufficiently reliable adhesion between the carrier tape and the cover tape.
Considering the demand for improved productivity and the change of material for the cover tape as described above, proposals have been made to conduct heat-sealing of cover tape to carrier tape, which has been done at a heat-sealing temperature of 120 to 160° C., at a higher temperature of about 180 to 220° C.
It is noted that a cover tape having, between a base layer and a heat-sealing layer, a cushion layer formed of linear low density polyethylene, elastomer resin, ethylene vinyl acetate copolymer or other flexible resin has been widely used, to provide cushioning characteristic and to improve heat-sealing characteristic (see Patent Document 1).
While the heat-sealing temperature becomes higher as described above, if the cushion layer has low softening temperature, the cushion layer resin would flow out from a tape end during heat-sealing, possibly causing a problem of contamination of a sealing bar used for heat-sealing. In addition, if the cushion layer has low softening temperature, thickness of cushion layer resin decreases as the cushion layer resin flows out, causing a problem of degraded strength of the cover tape itself.
If a resin having high softening temperature is used in order to prevent the outflow of cushion layer resin, the cushion layer would not sufficiently be made soft even when heated for heat-sealing, so that the heat-sealing layer would not well follow any warp, deformation or roughness on the surface of the carrier tape, and as a result, sufficient adhesion between the heat-sealing layer and the carrier tape would not be attained, causing a problem of lower peeling strength (adhesion strength). In view of these problems, development of a cover tape that can suitably be used at a high heat-sealing temperature of 180 to 220° C. has been desired.